JPH0661822A - Switching transistor drive circuit - Google Patents

Abstract

PURPOSE:To prevent a malfunction due to an undershoot at an output terminal by providing two NPN transistors(TRs) and a constant current source in an IC. CONSTITUTION:When an output Vout of a push-pull circuit changes from a high level to a low level, an undershoot in which a voltage swings to negative side only at the moment may take place because of an L component of wiring at an output terminal 7. Thus, a parasitic TR is caused in a semiconductor integrated circuit and the circuit may malfunction. When a TR 1 is turned off and a TR 2 is turned on and an output terminal 7 goes to a low level, a TR 3 is turned on by a constant current source 9 and a TR 4. In this case, a voltage Vout at the output terminal 7 is expressed as Vout=VBE4-VBE3 (VBE4 is a base-emitter forward voltage of the TR 4 and VBE3 is a base- emitter forward voltage of the TR 3). Since the relation of VBE3=VBE 0.7V is in existence, the voltage Vout is 0V and is not decreased more. Thus, malfunction due to undershoot at the output terminal 7 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching transistor driving circuit using a push-pull circuit, and more particularly to a circuit for preventing a malfunction due to occurrence of a parasitic transistor when an output terminal voltage becomes lower than a ground voltage.

[0002]

2. Description of the Related Art In a conventional push-pull circuit for switching driving of a transistor, a collector of a transistor 1 is connected to a power supply VCC, an emitter of the transistor 1 is connected to a switching element 8, and a transistor 2 is connected as shown in FIG. The circuit is such that the collector is connected to the emitter of the transistor 1 and the emitter of the transistor 2 is grounded.

Here, the signals 1 and 2 of FIG. 6 are applied to the bases of the transistors 1 and 2, respectively.

Next, the operation will be described. When the transistor 1 is on and the transistor 2 is off, the state of the output (Vout) terminal 7 is High as shown in FIG.
When the transistor 1 is OFF and the transistor 2 is ON at the (VCC) level, the state of the output terminal 7 is as shown in FIG.
It becomes the Low (GND) level shown in.

However, since the output terminal 7 actually has an inductance (L) component due to the wiring, an undershoot W phenomenon in which the output potential becomes lower than the GND potential occurs as shown in FIG. This is called undershoot, and in the semiconductor integrated circuit, the collector (epitaxial region) becomes lower than the substrate, causing the parasitic transistor to operate. When this parasitic transistor operates, it causes a malfunction.

Therefore, the anode side of the Schottky barrier diode 10 as shown in FIG. 3 is connected to GND, and the cathode side is connected to the output terminal 7. Since the VF of the Schottky barrier diode 10 is about 0.4V, the Schottky barrier diode 10 conducts at [Vout-0.4V] and the potential does not drop further. In this way, the potential of the output terminal 7 was prevented from dropping. This potential does not cause malfunction in the semiconductor integrated circuit.

[0007]

The conventional push-pull circuit shown in FIG. 3, which is usually a semiconductor integrated circuit, is used for the purpose of preventing malfunction due to undershoot of the output terminal 7 as described above. Although the barrier diode 10 is used, there is a problem that the cost is increased because the number of parts is increased.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, to provide a switching transistor drive circuit which prevents malfunction due to the adder shoot phenomenon without increasing the number of parts and increasing the cost.

[0009]

The first structure of the present invention is as follows.
In a switching transistor drive circuit for driving a switching element with an output terminal of a push-pull circuit connected between first and second power supply terminals, a collector and a base are commonly connected, and an emitter is the second power supply terminal. A first transistor connected to the first power supply terminal, a constant current source connected between the collector / base connection point of the first transistor and the first power supply terminal, and a collector connected to the first power supply terminal at the base. A second transistor of the same conductivity type as that of the first transistor, each of which is connected to a collector-base connection point of the first transistor, and an emitter of which is connected to an output terminal of the push-pull circuit; It is characterized in that a clamp circuit is provided.

A second structure of the present invention is connected between a first transistor having a collector and a base commonly connected, and a collector-base connection point of the first transistor and a first power supply terminal. A constant current source, a series body of one or a plurality of transistors whose collector and base are commonly connected between the emitter of the first transistor and the second power supply terminal, and the collector is connected to another power supply terminal. And between the second transistor whose base is connected to the collector-base connection point of the first transistor, and the emitter of the second transistor and the output terminal of the push-pull circuit. In the same number as the series body of transistors,
A clock circuit having one or a plurality of transistors of the same conductivity type and the same connection is provided.

[0011]

1 is a circuit diagram showing a switching transistor drive circuit according to a first embodiment of the present invention. In FIG. 1, the switching transistor drive circuit of the present embodiment is
In a switching transistor drive circuit in which a switching element 8 is driven by an output (Vout) terminal 7 of a push-pull circuit connected to both ends of a power source (VCC-ground),
A first transistor 4 having a collector and a base commonly connected and an emitter connected to the other end of a power supply, and a constant current source 9 connected between a collector-base connection point of the first transistor 4 and one end of the power supply. Of the same conductivity type as the first transistor 4 in which the collector is connected to one end of the power supply, the base is connected to the collector-base connection point of the first transistor 4, and the emitter is connected to the output terminal 7 of the push-pull circuit. It is characterized in that it has a clamp circuit composed of the second transistor 3.

In the push-pull circuit, the collector of the transistor 1 is connected to the power source, the emitter of the transistor 1 is connected to the collector of the transistor 2, the emitter of the transistor 2 is grounded, and the bases of the transistor 1 and the base of the transistor 2 are connected to each other. A circuit for alternately inputting a signal for turning on the transistor and a signal for turning off the transistor (FIG. 6) is connected, and the collector of the transistor 2 is used as an output terminal 7. The output terminal 7 is connected to the external switching element 8 and is supplied from the power source. The current source 9 is connected, the collector and the base of the transistor 4 are connected to the constant current source, the emitter of the transistor 4 is connected to the GND, the collector of the transistor 3 is used as the power source, and the base of the transistor 3 is connected to the constant current source and the transistor 4.
Is connected to the intersection of the collectors of and the emitter of the transistor 3 is connected to the output terminal 7.

Now, when the transistor 1 is turned on, the transistor 2 is turned off, and a current flows into the output Vout,
Vout is in the High (potential of the power supply voltage) state shown in FIG. Further, when the transistor 1 is turned off, the transistor 2 is turned on, and a current flows from Vout to the transistor 2, and Vout is Low (GND) shown in FIG.
It becomes the state of.

When Vout changes from High to Low, as shown in FIG. 5, because of the L component of the wiring at the output end,
If the voltage fluctuates negatively for a moment (undershoot), a parasitic transistor may be generated in the semiconductor integrated circuit, and the semiconductor integrated circuit may malfunction.

Therefore, when the transistor 1 is turned off, the transistor 2 is turned on, and the output terminal 7 is in a low state, the constant current source 9 and the transistor 4 turn on the transistor 3. At this time, the voltage Vo of the output terminal 7
ut can be calculated by the following equation.

Vout = VBE4-VBE3 where VBE4 is the base-emitter forward voltage of the transistor 4, and VBE3 is the base-emitter forward voltage of the transistor 3.

Since VBE3 = VBE4.apprxeq.0.7V, Vout becomes 0V, and does not fall below that.

FIG. 2 is a circuit diagram showing a switching transistor drive circuit according to the second embodiment of the present invention. In the push-pull circuit shown in FIG. 2, the collector of the transistor 1 is used as a power source and the emitter of the transistor 1 is used as the transistor 2
Connected to the collector of the transistor 2, the emitter of the transistor 2 is grounded, and the base of the transistor 1 and the base of the transistor 2 are connected to a circuit in which a signal for turning on the transistor and a signal for turning off the transistor (Fig. 6) are alternately input. , The collector of the transistor 2 is used as the output terminal 7. The output terminal 7 is connected to the external switching element 7, the constant current source 9 is connected from the power source, the collector and the base of the NPN transistor 4 are the constant current source 9, and the emitter of the NPN transistor 4 is the emitter of the PNP transistor 5. The PNP transistor 5 has its collector and base connected to ground. Further, the collector of the NPN transistor 3 is used as a power source, the base of the NPN transistor 3 is connected to the intersection of the constant current source 9 and the collector of the transistor 4, the emitter of the NPN transistor 3 is connected to the emitter of the PNP transistor 6, and the PNP transistor is connected. The base and collector of 6 are connected to the output terminal 7.

In the operation of the first embodiment, when the power supply voltage is high and the voltage Vout is too high, the EB reverse withstand voltage of the NPN transistor 3 is low, so the NPN transistor 3
There is a possibility that the transistor will be broken down between the emitter and the base, and the transistor will be deteriorated or destroyed. Therefore, in the present embodiment of FIG. 2, by adding a PNP transistor having a higher EB reverse breakdown voltage than the NPN transistor, the reverse breakdown voltage is applied between the EBs of the transistor 3 and the like even when the power supply voltage is high, causing a breakdown. The stable undershoot can be prevented without breaking.

[0020]

As described above, according to the present invention, by providing the clamp circuit composed of at least two NPN transistors and the constant current source in the semiconductor integrated circuit, the malfunction due to the undershoot of the output terminal is prevented. Since it can be prevented, it is not necessary to use the conventional Schottky barrier diode, and there is an effect that the cost can be sufficiently reduced without increasing the number of parts.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a switching transistor drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional switching transistor drive circuit.

FIG. 4 is an output waveform diagram showing the operation of the circuit of FIG.

FIG. 5 is an output waveform diagram showing a state when no malfunction prevention measure is taken.

FIG. 6 is a pair of input waveform diagrams of the push-pull circuit.

[Explanation of symbols] 1,2,3,4 NPN transistor 5,6 PNP transistor 7 Output terminal (Vout) 8 Switching element 9 Constant current source 10 Schottky barrier diode W Undershoot

Claims (2)

[Claims] 1. A switching transistor drive circuit for driving a switching element at an output terminal of a push-pull circuit connected between first and second power supply terminals, wherein a collector and a base are commonly connected and an emitter is said A first transistor connected to a second power supply terminal, a constant current source connected between a collector-base connection point of the first transistor and the first power supply terminal, and a collector connected to the first transistor.
A base is connected to a connection point between the collector and the base of the first transistor, and an emitter is connected to an output terminal of the push-pull circuit,
And a second transistor of the same conductivity type as the clamp circuit. 2. A first connection in which a collector and a base are commonly connected.
Transistor, a constant current source connected between the collector / base connection point of the first transistor and the first power supply terminal, and between the emitter of the first transistor and the second power supply terminal. A series body of one or more transistors whose collectors and bases are commonly connected, and a second transistor whose collector is connected to another power supply terminal and whose base is connected to the collector-base connection point of the first transistor. And, between the emitter of the second transistor and the output terminal of the push-pull circuit, the same number and the same conductivity type as the series body of the one or more transistors,
A switching transistor drive circuit is provided with a clock circuit including one or a plurality of transistors that are connected in the same manner.